Photographic screen for half-tone work.



I. W. MORRIS.

PHOTOGRAPHIC SCREEN FOR HALF TONE WORK.

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I Atty I' part thereof.

En srarns `Parleur @Erica JAMES WILLARD MORRIS, NEW YORK, N. Y., -ASSIGrNOIIR, T0 THE SINPAR COMPANY,

. f A CORPORATION OF NEW YORK.

PHOTOGEAPHIC SCREEN Foa nenn-TONE WORK.

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Specification of Letters Patent.

Patented Nov. 2a, 1ers.

Application led .Tune 24, 1909. Serial No. 503,983.

city, county, and State of New York, have invented certain new and useful Improvements in"`Photographic Screens for AHalf-v Tone lvoi-k, of which the following is a specication, reference being had therein --to the aecompanylng drawings, wlnch; 'form a My invention-"relates v.to photographic screens for half-tone work and more particularly to suoli screens as articles of manufacture.

In making half-tones in accordance with practices now generally followed in photoengraving, the subject is first photographed upon an ordinary photographic plate and a negative developed. A positive, either upon an enlarged or a reduced scale, is then made from this negative and after retouching, a second negative plate, called a screened negative, is made by photographing with a screen interposed between the positive and the sensitized plate. From this screened negative the sensitized metallic plate is printed and developed prior to the acid etching. In all 'of these steps excepting'when exposing the metallic plate a camera 1s used. For printing purposes' the iat tones of the photograph must be interrupted in the negative to reproduce these tones upon the vetched plate by means of dots,either black or white, making respectively inked surfaces and the indentations about same necessary in ordinary printing. At the present time this interruption of the tones upon the last negative is accomplished by means of a transparent plate havingthereon fine, closely juxtaposed parallel lines extending at right angles to each other. which lines are opaque so as to intercept the light rays'passing through the camera lens and said screen to the sensitized plate for the negative. The action of these rays upon said plate and upon the metallic plate when printed from the negative is ident-ical with the ordinary photographic practice. or 'photographic art, setting the sensitizing agent upon the plate -where the .light penetrates and failing to set it where mits the acid to etch away the surface of the plate only at those points where the said agent was not set, causing depressions resulting in white dots at such point on an impression made from .the plate. The screensl heretofore `used have always pos: sessed'a well- .defined design which appears reproduced upon'- the negative and conse-f' I quently upon the sensitized metaljplate, and

upon the prints taken therefrom; and furthermore this well defined design results in fiatness in the prints, and a loss of that artistic effect desirable in high class work. To obviate this, the screens will sometimes have the lines very narrow and will run as high as 400 to the inchto secure a fine mesh and thus reduce as much as possible the prominence of the screen design upon the plate and the print taken therefrom.

In additionto the ruled screen above referred to, aglass screen known as the-Metzograph screen is sometimes used. In this screen, the effective surface is formed into a plurality of depressions varying in size, so that theadjacent portions of the resist upon the plate to be etched vary in size. Hence svhen .etching the plate, particularly for the high lights, the smaller dots etch entirely away with a result-ant isolation of the larger dots in a manner to give a poor tone effect.

The main object of the invention is to .provide a screen for half-tone work which will embgdy therein no set design and will reproduc upon thesensitized plate, a plurality of irregularly juxtaposed white and black spaces or dots to secure a suitable effect without any design whatever beyond the lights and shadows of the original itself. A further object is to provide a plate having a surface thereon composed of a plurality of juxtaposed minute lens-like formations in order that the said screen will have a lenticular effect upon the light rays at each point of penetration, and thus insure a well defined actionof this light upon the sensitized plate and avoid that diffusion of the light which occurs when concentrated light rays are passing through a flat glass plate as in the present practice in photo-engraving. A still further object is to provide av screen which will of itself have a focal distance with relation `to the sensitized plate. A still further object is to pro` 4thel sensitized plate by direct or paral lel light rays as distinguished from such rays passing through an interposed lens. And a. still further object is to provide a.

5- photographic screen which will not only j simplify the process of photo-engraving, but will give improved artistic effects as compared with the products' of practices now being commonly followed. through the .l strengthening of the lines in the reproduca transparent film composed of irregularly j disposed adjoining dissimilar surfaces, the alterna-te surfaces having lens-like formation whereby the light rays falling thereon will be refracted into fociand a stippled effect will be produced upon a 'sensitized plate; and in'such other novel features of construction and combination ofqparts as are hereinafter set forth and described and more particularly pointed out. in the claims hereto appended. n Referring to the drawings, Figure 1 is a view of the top of a screen plate. a portion 0 -of the surface thereof having .indicated thereon the character ofthe film. only a portion of the surface showing this film. however` and Fig. 2 is a cross section of a portion of the screen'sliowing it arranged wit-hin focal distance of a sensitized plate. the film being shown upon ya greatly magnified scale and approximating its cross-section. as seen through a powerful microscope` the refraction and concentration of the light rays be- 10 ing indicated in dotted lines.

Like letters refer to like parts in both of said views.

My -improved photographic screen. as"

illustrated in the accompanying drawings,

consists of a transparent or translucent sur-l face a preferably formed of a film mounted or deposited upon a transparent support. as

plate of glass b. This glass is used solely as a protecting medium forthe film and 5f it is not my intention to. limit the inven-A tion in its broader aspectsto lthe use of a plate of glass, it being apparent that under some conditions the film a alone may be used. Opposed to the plate b` is a second 5 plate c protecting the other side of the film. The edges of the two plates b c may be secured in any desired manner as by the passe-partout strip (Z. A j

This film a. is composed of gelatinous material which yI subjectto an asti'infrent having the effect of contracting the mass of the material to form a plurality of closely juxtaposed adjoining surfaces. the said surfaces being alternately concave as at e and cons vex as at f and the concave and convex surfaces being formed by a reverse curve so .anv light through that point upon the sensitized plate. The concavities in the film, 80 form plano-concave lenses which serve to diverge the light rays to focus\with the rays through the adjoining plano-convex surfaces, thus permitting the use of the screen with the same effect. Hence the entire film 8 is translucent or transparent serving in adjoining minute spots to project or diverge the light rays as they are admitted therethrough to the negative photographic plate.

The .number of conca-vities and convexities contained within any predetermined space will control the texture of the stipple effect produced thereby, by increasing the number of contrasting dots in said space..thus're ducing the size of the dots and increasing their number. A

To avoid the presence of a design upon the film which design will be reproduced to al certain extent upon the sensitizedplate. Iv arrange this surface irregularly. alternating, concavities and convexities, however. as above described. thus avoiding a similar design throughout the entire plate and pro-l ducing an effect similar to the ordinary stippling. This irregular arrangement is clearly illustratedin Fig. 1. This plate so made becomes a master plate and the design thereof andthe tone of this design may be reproduced upon a plate having alight sensit-ive lm. phojtographically to produce succeeding plates. v

In using the screen several practices may be followed'. It may be used as the ordinary ruled screen.. that is. mounted within a camera so as to concentrate portions of the, light rays passing from the lens through the screen to the sensitized plate. This plate, however. differing from the manner of use of the ruled screen, may be used with any parallel rays of light either natural or artificial, to print directly. from a' negative upon a sensitized metallic plate. by interposlng a screen at the proper focal distance between-the negative and the light or hetween the negative and the sensitized plate.

This adaptability to this use is due entirely to the fact of the lenticular eti'ect of the alternate concavities and convexities in the screen. which. when it is placed at the proper focal distance from the sensitized plate, act 130 as a multitude of small lenses to concentrate the light rays and pass them through the negative in variable lvolume at different points upon the sensitized plate thus setting the sensitizing agent upon said plates in the same manner as 'with an ordinary photographic plate upon a sensitized paper.

The absence of opaque lines in my im- 'i proved screen permits a greater volume of p 20 In producing the irst, or master, plate, a'

transparent support, as a plate of glass, is coated with ordinary gelatin in the usual manneremployed in coating photographic dry plates. No chemicals need be mixed with the gelatin; and the best results have been secured by the use of pure gelatin. rllhis plate is then submerged in a Warm solution containing chromic acid, tannic acid, formaldehyde, bromid .of potassium or any equivalent astringent which will have the effect'of contracting or tanning the gelatin. The solution may vary in temperature from 90 to 145 degrees Fahrenheit, good results having been secured at both these temperatures and at many intermediate telnperaturesQ When the. gelatin has been contracted or tanned to the desired extent, which is determinable only, by a sense of feeling, developed by experience, the plate @o is removed` from the astringent bath; washed with clear water to arrest the action of the astringent, and dried under a gentle `heat.

It has been found that the astringent used n and the temperature of the bath vary* with the different plates, and that the texture of, succeeding plates will vary when treated `under identi'cal conditions. Infact, the production of the plate does not seem susceptible to reduction to a fixed rule either as to theastringent or as' to the temperature. This erratic action of the gelatin, under treatment, is attributed to different qualities or conditions present in different lots of gelatin. Good results have been secured when a; large number of .plates were coated with the same lot of gelatin, and the best treatment for the lot of plates determined by experimentation with a few of them. ln 80 fact, so many conditions arise, such as the age of the plates, .the climatic conditions, the Y thickness of the gelatin, variationsinsuch thickness on a plate, slight ,variation of temperature o f. the bath and even the degree of purity ofthe astringent used, all of which necessitate a change-in the treatment of the coated plate, that the skill of the Workman is required yto adapt the treatment to the varying conditions. Under the niost favorable conditions, the number of perfect plates have not exceeded l0 per cent. of those e treated, and with plates above 14x17 inches,

the percentage is even lower because of a lack. of uniformity in the action of the astringent throughout the entire surface of the gelatin. The time of t1eatment""\vill varylwith the strength of the solution, the temperature of the bath and other conditions, the exact nature of which cannot be determined. At times a plate will respond "Se within a minute, while at other times sev-v eral minutes are required. At times, of-two plates treated under the same conditions, one following the other, 'one will respond quickly, while the other will require a much longer time'. The action ofl'the astringent is erratic, and the nature of plates produced is also erratic. No fixed law for producing a plate of a given texture can possibly be laid down. A y i With my improved screen an ordinary photographic negative, as g in the drawings` is placed upon or 'in close juxtaposition to the sensitized printing surface indicated at it, as a metal plate and a screen interposed at the proper distance from the printing surface tov focus each of the lens-like formations of the. screen upon said surface. All of these lens-like formations .being substantially the same, the lscreen is always used at- 10G a certain distance from the printing surface, which` is its screen distance. Diiferent artistic .effects may be secured by using the screen at a distance Where it will be slightly out of focus or in focus. The plate is then '105 exposed to light, either through a camera lens or to parallel rays. The light passing through the screen will penetrate the transparent or translucent tones of the negative, the rays focused by each lens like formation, settingy the sensitizing agent upon the printing surface and thus preventing the etching of this portion and producing a sharp black dot varying in size with the volume of light passing through the negative, the light tones in the negative producing a number of closely juxtaposed high dots upon the sensitized printing surface, which dots will be separated by wavy, depressed, irregular lines. 'Where the tones on the negative are 123 very light these dots will run together to a certain extent into wavy high lines and where the tones on the negative are darker, less light will be permitted to penetrate and 'there will be a proportioned diminishment 12:

in the size and number of the high dots with the broadening of the intervening depressed wavy lines. The tones of the negative are thus preserved on the printing surface, the subsequent. treatment of the printing sur- 1&6

a a positive' taken therefrom.

face removing said surface where tliesensitizing 'agent was not set, in the usual and Yextent and this variance will be controlled not by the screen itself but by the tones of the negative or of the subjectbeing reproduced. Hence while to a certain extent'the pattern of the screen will appear upon the plate, nevertheless, it will never be the same in any two plates and will loose that characteristic'of `a well defined design which is apparent even to the naked eye in the ruled or lined screen.

lith vscreens made inaccordance with my invent-ion, it is possible to print a sensitized printing siii-face directly from the negative of a snap-shot photograpln'as well as from Furthermore, the artistic characteristics of the ordinaryT negative are not lost through a reproducing process and in printing upon the sensitized printing surface. The transparent nature of my screen -in its entirety permits an increase iii yolume of light 'passing through as compared' with semi-opaqiie screens to an extent to secure a clear reprovduction or print from the negative with a short exposure and 'a more accurate tone rendering. A further advantage is that those portions o f the screen which deflect` the light, in printing direct, result in depressions in the sensitized plate of a character to intensify the shadows-in theprints therefrom and subordinate the screen effects to the tones of the negative. A still further advantage is that Vby reasonof the screen itself having a lenticulareffect, or a focus co-inciding with its screen distance, diffusion -of the ,light passingA through the screen and a negative in printing the sensitized printing surface is obviated. thus having a strongtendency to make the etched printing surface sharper than an original printed from the negativeitself. It will be observed that with this print-ing surface the steps incidental to making a screened negative, ai'e'eliminated as with an original negative. a photo-engraved printing surface 'may be produced without the aid of a.

camera and with a resultant reduction in the time required in making the photo-engraved plate.

It is not my intention to limit the invention to the precise detailed const-ructionof the plate as shown in the accompanying drawings` it being apparent that such may be modified without departing frm the spirit and scope of the invention. I believe.

it to be broadly new to provide a screen for `sensitized plate and I intend to opaquev surfaesiand a surface adapted to focus light passed therethrough upon the claim )such broadly. A

Having described the invention, what 'I claim as new, and desire to have protected by Letters Patent, is y l'. As Ia new article of manufacture, a

photographic vscreen for half-tone work, em-

bodying therein a transparent film having minute irregularly. disposed, adjoining, dissimilar, lens-like surface formations, whereby' light rays will'be iefracted into 'and focused by alternate formations, to produce a stippled effect upon a sensitized surface.

2. As a new .article of manufacture, a photographic screen for half-tone work, embodying thereina transparent film having irregularly disposed minute curved surface formations whereby light rays will be fosol cused through alternate surface formations A to produce a st-ippled effectupon a sensitized surface.

3. As a' new article of manufacture', a photographic screen for half-tone work embodying therein a transparentsupport and a transparent film thereon having irregu therein a plurality of irregularly disposed minute convex surface formations, whereby light rays will be focused at a plurality of f,

closely juxtaposed points upon a sensitized surface to produce a stippled effect.l

5. As a new article of manufacture, a

' photographic screen for half-tone` work, em-

bodying therein a transparent film having therein a` plurality of irregularly disposed closely juxtaposed alternate minute concave and convex surface formations, whereby light rays will be refracted into and focused by alternate format-ions to produce a stippled effect upon a sensitized surface.

`6. As a new article of manufacture, a

photographic screen for half-tone work, em-

bodying therein a transparent support and a transparent film thereon,'s,aid film having therein a plurality of irregularly arranged, minute convex surface formations whereby light rays will be focused at a plurality of closely .juxtaposed points upon a,A sensitized surface to produce a stippled effect;

7. As a new article `of manufacture, a photographic screen for half-tone work, ernbodying therein a transparent support and a transparent film thereon` said film having therein a plurality of closely juxtaposed alternate irregularly arranged. minute Vlenslikesurface formations, whereby light vrays will be refractecl into and focused by alters.

nate formations to produce a-stippled effect upon a sensitized surface.

8. As a new article of manufacture, a photographic screen for half-tone work, embodying therein a transparent support and a transparent film having therein a plu- `rality of minute, closely juxtaposed, irregularly disposed' curved surface formations,

`whereby light rays will be focused by alternate surface formations to produce a stippled effect upon a sensitized surface, and a 4transparent protecting sheathing for said film.

9. As 'a new article of manufacture, a photographic screenA for half-tone work, em-

bodying therein a transparent film having therein a plurality of minute, lrregularly arranged convex surface formations whereby the light rays will be focused at a plurality of closely juxtaposed points upon a sensif tized surface toproduce a stippled eHect, and a transparent protecting sheathing for said iilin.

.10. As a new article of manufacture, a

photographic screen for half-tone work comprising a transparent plate having a surface composed of a plurality-'of irregularly arranged minute lens-like surface formations, whereby light rays will be refracted into and focused by alternate formations to produce a stippled effect upon a sensitized surface.

11. A half-tone screen comprising a ilm having a surface formed with irregularly disposed reversely curved portions-constitutinga pattern dissimilar in different portions thereof, and which will refract light rays passing therethrough to produce a stippled effect upon a sensitized plate when exposed thereunder.

In witness whereof, I have hereunto affixed/my signature this 18th day of June, in the presence of two witnesses.

JAMES WILLARD MORRIS.

Witnesses:

P. V.' WENING, P. FRANK SONNEK. 

